Crystal drier



Feia. 8,1949%. J. M. WOLFSKILLM 2,451,489

, CRYSTAL DRIER Filed NW. 17, 1944 Y s sheets-she t 1 Feb. 8, 1949. J. M. WOLFSKILL 2,

QRYSTAB DRiIER I Filed Nov. 1?, i944 3 Sheets-Sheet s goo fiesqus/vcy Cl/A/YGF- Crass 2 3 4 J 6' 7 8 9 /0 ll 3 CRYSTAL Humane i/ n a? FREQ us/vcy CAM/V65 CYCLES CRYSTAL NUMBtE Clever/14 Iva/wan? Jam /Mm Patented Feb. 8, 1949 warren: STATES? oer-ice CRYSTAL DBIERi John lvIlUWolfskill, Erie, i aggassignorito "Blily 7 Electric Company; Erie;- Pal, acorporatiohof Pennsylvania Application November 1'7, 1944,--Serial;No. 563,966..

' 5 Claims. (oi. 34=-58")' narilygroundtcapproximate dimensions in lappingimachines after which the crystals are fur ther. reduced in size. to bring thein to. a desired frequency eitherby handllappinglor etching operations. After. the machine lapping operations, the crystals are usuallytestedior frequency in an oscillator circuit and. edge ground to bring them to maximum. activity, the latternoperation frequentiy requiring.severalftests in. the oscillator circuitfwhen hand lapping operations are em-. ployed'to bringtheicrystal .to desired frequency and activity, repeated tests in the oscillator circuitv are usually'required. in carefully controlled 1 etching operations the number-of frequency tests required. is considerably. less. than that. for hand lapping. operations, but, nevertheless, a plurality of. frequency and. activity testsmust usuallyibe I made... Prior tosuoh tests the abrasive and carrier therefor. or residual etching solution must be washed from thecrystal surfaces andjthecrystal then dried; Itwillthus be seen thatinthe manufactureof piezoelectric crystals frequent washing. andldr ing operationsinust be carried out.

Any. appreciableamount of foreign material adheringto a crystal will modify the characteristics offtheicrystal. Thus, lint from towels used inidr'yinfg the crystal or solid materialsin solution or suspension in water and deposited on the crystal durin dryingof the waterwill, in. general,-1ower the frequency of the crystal anunpredictable amount or otherwise modifyits .characteristics.

Various methods .of drying crysta1s.after.wash-. ing and rinsing andprior to testing have been employed by the art. Of these, probably the most cases',,'ordinary. laundry. towels have. been employed butusually special types; of towels such as. lint free towels. paper .towels and blotting paper havebeen used. The results obtained, however, were. extremely variable. They depended upon the..genralrleanlin'ess 0f the'towel itself, how long'it'hadh'een in use, and in the case of. laundry towels .the,manner.in .whichit had been laun deredf'for'exampl'e, the'type of soap used in testingjn an'oscillatcr circuit. Crystals are 'ordi-I common means of drying was by towels. .Insorne 1 laundering and thestarchcontent imparted to the towel... The lintv characteristics of the towel' were of particulanimportance as even small amounts of .lint'left on the crystal materially 'modified its operation. Becauseof thevariable results the art had; long recognized that even reasonably: clean. crystals ,Were in factnot being produced bydrying with towels Cither methods .of dryingincluding the employmentof. currents of heated. air from blowers having heating elementsassociated therewith and strong blastsof air. from sources of compressed air were tried. The.velecityjofairifrom blowers was not sufficient to blownalltof the rinse water from...the crystal" surfaces. Water was slowly evaporated thereon, ;l'eav-ing'- onthe face of the crystals any. solids ..in solution or suspension in the water. .These solids were irregularly depositedon the crystal suriac'e leaving water spots materiaily affecting the performance ofthe crystal. In

using hitihteloCiWQMasts from compressed air sources, .it'lwas poss'ible. to. blow off 'someof the excess water. after thje crystal was .rinsed. Ihe chief i difficulty with. .this method-0f -drying was, however, .that 'it was, not possiblaasa practical matter; to; obtain,a compressed airsource that was completely .free of moisture and ioil particles.

The solubles in dirty water from .a compressed air line and-oilparticles inthe air were irregularly and unpredictably deposited. on the crystal surface during drying-resulting in oil and water spots on 'suchlsurfaces. Attempts to filter the com- I press'ed air were not successful and consistent resultswere not. obtained.

In.accordance. with.,the present invention a Washed and'rinsed crystal is .properlysupported androtated.atan-extremelyhigh speed. Large .bodilyremoving. water with. its associated solids from the crystalsurfaces. The. resulting-crysta1 surfaces are substantially completely cleaned.

Andres; drying operation is ,much more rapid than those heretoforeproposed The crystal can ordinari-lybe completely dried; infromthree to five seconds.

It is therefore an objectof'the present inven-, tion. to provideianimprovedlinethod and apparatus-for drying piezoelectric crystals.

Anotherob'jectpf the inventionis toprovide a method ofdrying piezoelectric crystals in which '7 the crystal is spun at a rapid rate to throw off adhering water and cause drying air to effectively contact the surfaces of the crystal.

Another object of the invention is to provide an improved drying apparatus for piezoelectric crystals which facilitates rapid and easy mounting of the crystal in the drying device and removal of the crystal therefrom after drying.

A further object of the invention is to provide a crystal drying apparatus in which the crystal is held in a manner enabling rinse water to flow rapidly from the surfaces thereof.

A still further object of the invention is to provide an improved crystal drying apparatus in which the crystal is spun about an axis passing through the body of the crystal.

Other objects and advantages will appear in the following description of preferred embodiments of the invention illustrated in the accompanying drawings, in which:

Figure l is an elevation of a drying apparatus with certain parts broken away;

Figure 2 is an isometric view of the crystal holding element shown in Figure 1;

Figure 3 is a view similar to Figure 2 showing a modified type of crystal holding element;

Figure 4 is a view similar to Figure 2 showing a further modified type of crystal holding element;

Figures 5a to 50, inclusive, are graphs showing the results of drying crystals by contact with towels; and

Figures 6a to 60, inclusive, are graphs similar to Figures 5a to 50 showing results of dryin in accordance with the present invention.

Referring to the drawings, Figure 1 shows a complete drying apparatus in accordance with the present invention. This apparatus may include a motor Ill, shown in the drawings as being an air motor mounted with its shaft II in a vertical position, the shaft II carrying a chuck I2 at its upper end. The internal structure of the motor Ill is not shown as such motors are available on the market in various forms, the particular motor shown being capable Of rotating as fast as 20,000 R. P. M., and being provided with a compressed air inlet conduit I3 and a speed regulating screw I4. The motor may be started and stopped by means of a valve I5 in the air inlet line IS, the valve being shown as a rotary valve normally held in closed position by a spring I5 and provided with an operating lever such as a foot pedal I6 for opening the valve against the action of the spring I5. While an air motor is shown, it will be understood that a high speed electric motor, also commercially available, can be employed in conjunction with a starting and stopping switch, if properly shielded, the chief disadvantage of high speed electric motors being that they frequently produce radio frequency interference which may cause difi'iculties in carrying out certain test procedures in crystal manufacturing operations.

The chuck l2 may receive the shank I6 of a crystal carrier I I. The crystal carrier shown in Figures 1 and 2 may include a cross member it carried by the shank I 6 and supporting a pair of wire loops I9. Each of the wire loops I9 preferably includes vertically extending parallel portions connected at their tops by an outwardly extending loop portion 29. The wire loops I9 may be secured to the cross member Is in any desired manner, for example by inserting their lower ends in bores 2|, one of which is shown in Figure 2 and soldering or brazing the wires in such 4 bores. The wire loops I9 are preferably made of relatively stiiT spring metal and as shown in Figure 1, the wire loops I9 provide a recess for receiving a crystal 22 to be dried.

It will be apparent that the crystal 22 may be easily inserted between the wire loops I9 by sliding the same downwardly therebetween and removed by merely lifting the crystal from the recess between the wires. While the wire loops I9 may fit the crystal sufiicientl close that they must be sprung apart slightly to insert the crystal, it is preferred to mount the c ystal loosely between the wires. When the crystal holder is rotated at a high speed, the crystal moves slightly off center and is held snugly against one of the loops by centrifugal force. There is then no danger of chipping the crystal while inserting or removing it. The crystal holdin means described presents substantially unobstructed paths for liquids thrown from the crystal surfaces by centrifugal force due to rotation of the crystal.

To guard against any possibility of injury to operators by reason of the crystal being thrown from the crystal carrier during rapid rotation, it is preferred to surround the crystal carrier by a stationary open topped screen 23, the screen being preferably a cylindrical member of solid sheet material although it may be of foraminous material. The screen 23 may be mounted on a base member 24 in turn supported by brackets 26 secured to the casing of the motor ID in any desired manner. Even if the possibility of a crystal being thrown from the carrier is remote, crystals sometimes shatter when being rapidly spun and the screen 23 prevents injury to operators due to particles of the glass-like materials of the crystal being thrown off at high speed.

The modified type of crystal carrier shown in Figure 3 is designed to prevent any possibility of a crystal being bodily thrown from the crystal carrier during rotation thereof. In the modification of Figure 3, the cross member 21 mounted on the shank IE and carrying the wires I9 may be provided with bearing members 28 extending from one longitudinal edge thereof. A pivoted guard member 29 may be journaled in the bearing members 28 and be provided with a crystal guard portion 3I at its upper end and a weight member 32 at its lower end. The guard portion 3I extends over the top of the crystal 22 when the weight member 32 is caused to move outwardly from the shank I6 due to centrifugal force during rapid rotation of the crystal carrier. It is not necessary that any portion of the member 29 actually contact the crystal when the crystal is in its normal position in the carrier. That i to say, the device is preferably constructed so that the pivoted member 29 engages the cross member 27 as a stop prior to contacting the crystal. This structure, however, obviates any possibility of the crystal being thrown bodily from the crystal carrier.

Another modified form of crystal carrier is shown in Figure 4. This crystal carrier may include a cross member 33 provided with a Wire loop IE3 at one end thereof and with projecting bearing members 34 at the other end thereof. A weighted member 36 may be journaled in the bearing members 34 and carry a weight 31 in its lower end. A spring wire loop 38 may be suitably secured to the upper portion of the weighted member 36. The wire loop 38 may have a form similar to the loop wire I9. Upon rotation of the crystal carrier shown in Figure 4, the weight 31 moves outwardly from the shank I5 and' th'e difference between the original frequency.

and the frequency after washinganddrying "was" Plotted ai l tihenmnbers pf the vario s crystals in figure a.

The iiystals were then again washed and dried withi'ft e tov'vels and the results plotted in Figure 51? fThe sarrLe crystals were thenwashed and dljigd with f-toi'vels a third tinref'an d tharesults pljot d'liriF'igure 50. It will be noted that. the change for each of the three washings A reof "substantially the sameorder and that they variediinpredictably. As'a specific example; crystal number .2 increased its frequency by earl 8.09 cm. g the retwes e d v na decreased s frequency by over" 150 cycles inlth'e. second washing and drying operation and then increased its frequency by approximately 600 cycles in the third washing and drying operation.

A similar set of curves is shown in Figures 6a, 6b and 6c. The same type of crystals were employed but instead of being dried by towels after washing were dried in accordance with the present invention. As was to be expected, the results of the first operation showed considerable variation as removal of foreign materials from the surface would be expected to increase the frequency of the crystal. The second and third washing and drying operations provided much more consistent results, the third drying operation, shown in Figure 6c, exhibiting very little change in frequency. This can only be explained on the basis that the first washing and drying operation substantially completely cleaned the crystal and that very little foreign material was either deposited upon or removed from the crystals in the second and third washing and drying operations. In fact, the maximum frequency change for any crystal during the third washing and drying operation was approximately 100 cycles, whereas the third washing and drying operation using towels, shown in Figure 50, resulted in several of the crystals exhibiting frequency change of approximately 600 cycles.

The curves of Figures 6a,, 6b and 60 thus illustrate that the drying operation of the present invention produces extremely clean crystals.

q to 5c illustrate v the 1 w e eb means of curveswwere derived from. data water; .0175. the crystal.;surfaces ljare; developed b self} an ..be carriediout extremely rapidly.

ristal? long period of t can c d .ingp

e v es i e. rinsedcrystalbetw e wires it on the crystal, carrier,. 'aiidf then rotate this crystal carrier at highfs-peedfforga few s ccondsfspeeds-.of from 15,000 to" 20,0 90, M have becn foundparticularly suitable. wee-nin axis} of rotation passes; 1 through the crystalalthough lower speeds -.dowr1;.-. tolfapproximately 5,900 B. P. M, can bejemployed viiithiefilefiwe results. l Ingeneral, the higher thei style d th molj-qllicklythe crystalis dried and the lessforeign materialis left upon thecrystah e; fiee i t llith eimnd a xtr i eeds. wi h h ryst l lee fil i t d. c setet c otation produ ce the ,best results. The crystal actsafsQ-a ll paddle wheeltoaccelerate the. air in itsfvicinity and cause ,rapid. currents affair, to, sweep the 'sidesoiof the crystal. Also stresses'in the crystalstruc'ture rela-.

tit e. to thebentrrf gal fforcef av ailable ,.to ithro r r rotating the, crystal .at high speed about an axis}. Q passing through the body of thecrystal, although a no "to meim t ea veta snbstantiel ve oif"ccn't er and employ lower speeds'of rotation? While I have disclosed the preferred embodiments of my invention, it is understood that the details thereof may be varied within the scope of the following claims:

I claim:

l. A devicefor drying piezoelectric crystals after washing, which comprises, a high speed motor having a shaft extending vertically upwardly therefrom, a crystal carrier mounted on said shaft, said crystal carrier having upwardly extending wire loops forming a recess for receiving said crystal to provide substantially unobstructed paths for liquid thrown from the surfaces of said crystal by centrifugal force, said loops being positioned to hold said crystal with its major surfaces substantially in vertical planes and with the axis of said shaft passing through said crystal.

2. A crystal drying apparatus comprising, a crystal carrier provided with means for supporting a crystal to be dried, said means providing substantially unobstructed paths for liquid thrown from the surfaces of said crystal by centrifugal force, means including a motor for rotating said crystal carrier at a rotation speed between approximately 5,000 and 20,000 R. P. M. to throw said liquid'from said surfaces, said supporting means including a base member secured to said shaft, a pair of spring wire loop members having their legs spaced from each other and secured to said base member and their looped ends spaced from said base member, said looped ends being bent away from each other to provide a recess for receiving said crystal.

3. A crystal drying apparatus comprising, a crystal carrier provided with means for supporting a crystal to be dried, said means providing substantially unobstructed paths for liquid thrown from the surfaces of said crystal by centrifugal force, means including a motor for rotating said crystal carrier at a rotation speed between approximately 5,000 and 20,000 R. P. M. to throw said liquid from said surfaces, and a shield around said carrier to restrain projection of crystals or portions thereof in the event of shattering or loss of said crystals from said carrier, said supporting means including a base member secured to said shaft, a pair of spring wire loop members having their legs spaced from each other and secured to said base member and their looped ends spaced from said base member, said looped ends being bent away from each other to provide a recess for receiving said crystal.

4. A crystal drying device comprising, a crystal carrier, a rotatable shaft for supporting said crystal carrier, said carrier comprising a support member mounted on said shaft and having a pair of projecting wire loops having an opening for receiving said crystals; means including a high speed motor for rotating said shaft to throw said liquid from the surfaces of said crystal by centrifugal force during rotation of said carrier, a shield around said carrier to restrain projection of crystals or portions thereof in the event of shattering or the loss of a crystal from said carrier, and a guard member pivotally carried by said support member, said guard member having a guard portion movable to a guard position in the path of movement of said crystals from said opening for preventing accidental displacement of said crystal from said carrier during rotation of said shaft, said guard member also having a weighted portion for retaining said guard portion in said guard position by action of centrifugal force during rotation of said shaft, said carrier having means to prevent said guard member from contacting said crystal when said crystal is correctly positioned in said loops.

5. A crystal drying device comprising, a crystal carrier, a rotatable shaft for supporting said crystal carrier, said carrier comprising a support member mounted on said shaft and having a pair of projecting members providing anopening for receiving said crystals, means including a high speed motor for rotating said shaft to throw said liquid from the surfaces of said crystals by centrifugal force during rotation of said carrier, and a guard member pivotally carried by said support member and having a guard portion movable to a guard position in the path of movement of said crystals from said opening to prevent accidental displacement of said crystal from said carrier, said guard member having a weighted portion holding said guard portion in guard position by action of centrifugal force during rotation of said carrier, said carrier having means for preventing contact of said guard member with said crystal when said crystal is correctly positioned in said projecting members.

JOHN M. WOLFSKILL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 817,801 Pittock Apr. 17, 1906 817,802 Pittock Apr. 17, 1906 970,108 Pierman Sep. 13, 1910 1,010,511 Mesta et a1 Dec. 5, 1911 1,694,541 Harry Dec. 11, 1928 2,212,317 Friedman Aug. 20, 1940 2,218,165 Gaebel Oct. 15, 1940 OTHER REFERENCES Websters New International Dictionary, 2nd edition, 1937, page 2471. 

